Rapid quantification of amlodipine enantiomers in human plasma by LC‐MS/MS: application to a clinical pharmacokinetic study

A rapid, simple, specific and sensitive LC‐MS/MS method has been developed and validated for the enantiomeric quantification of amlodipine (AML) isomers [ R ‐amlodipine ( R ‐AML) and S ‐amlodipine ( S ‐AML)] with 200 μL of human plasma using R ‐AML‐ d 4 and S ‐AML‐ d 4 as corresponding internal standards as per regulatory guidelines. A simple liquid–liquid extraction process was used to extract these analytes from human plasma. The total run time was 3.5 min and the elution of R ‐AML, S ‐AML, R ‐AML‐ d 4 and S ‐AML‐ d 4 occurred at 1.62, 2.51, 1.63 and 2.53 min, respectively. This was achieved with a mobile phase consisting of 0.2% ammonia–acetonitrile (20:80, v/v) at a flow rate of 1 mL/min on a Chiralcel OJ RH column. A linear response function was established for the range of concentrations 0.1–10 ng/mL ( r >0.998) for each enantiomer. The intra‐ and inter‐day precision values for both enantiomers met the acceptance criteria. Both enantiomers were stable in a set of stability studies, viz. bench‐top, auto‐sampler, freeze–thaw cycles and long‐term. The current assay was successfully applied to a pharmacokinetic study to quantitate AML enantiomers following oral administration of 10 mg AML tablet to humans. Copyright © 2013 John Wiley & Sons, Ltd.